Cell lines from human mesotheliomas have been shown to express the platelet-derived growth factor PDGF-A gene product, while normal human mesothelial cells do not. Production of PDGF-B chain protein was not detected. A model cell was shown to be tumorigenic. This model was created by expressing the long-splice variant of human PDGF-A chain under the control of a Moloney viral LTR promoter in a non-tumorigenic, T-antigen immortalized human mesothelial cell. Analysis of the receptor-ligand interactions in this cell line, human mesothelioma cell lines and normal and T-antigen expressing, non-tumorigenic human mesothelial cells is underway. PDGFR-alpha but not PDGFR-beta expression is down regulated in mesothelioma as compared to normal mesothelial cells.